Multilayer metasurfaces have attracted much attention for broad bandwidth and high transmission efficiency. However, the electromagnetic (EM) coupling will be significant and greatly affect the transmission performance when the inter-layer distance is in subwavelength scale. Here, we present a generally equivalent circuit approach (ECA) that can be used to investigate the transmission performance and the near-field coupling mechanism in multilayer metasurfaces. Based on the proposed ECA, the analytical expression of transmission coefficient is obtained. The accuracy of the circuit model is further verified by several typical multilayer metasurfaces in ultrawideband from 0 to 30 GHz. The proposed method is valid for an arbitrary multilayer metasurface system, regardless of the layer number and the metallic elements.

中文翻译：

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具有近场耦合的多层超表面的精确半数值方法

多层超表面因其宽带宽和高传输效率而备受关注。然而，当层间距离处于亚波长尺度时，电磁（EM）耦合将显着并极大地影响传输性能。在这里，我们提出了一种通用等效电路方法（ECA），可用于研究多层超表面中的传输性能和近场耦合机制。基于提出的ECA，得到了传输系数的解析表达式。电路模型的准确性通过 0 至 30 GHz 超宽带中的几个典型多层超表面进一步验证。无论层数和金属元素如何，所提出的方法都适用于任意多层超表面系统。